Motor vehicle brake system

ABSTRACT

A differential includes a planet gear through which two shafts coupled to laterally spaced road wheels of a motor vehicle are interconnected. The planet gear has a rotatable shaft with a brake mechanism coupled thereto. A braking force produced by the brake mechanism is transmitted through the differential to the road wheels depending on the rotational speeds of the road wheels. The brake mechanism may include either a turbine for producing a resistive force upon rotation thereof or a hydraulic damper comprising a hydraulic pump and a variable restriction.

This application is a continuation, of application Ser. No. 07/578,237,filed Sep. 6, 1990, now abandoned, which is a divisional of copendingapplication Ser. No. 07/440,248 filed on Nov. 22, 1989, now U.S. Pat.No. 5,031,738.

BACKGROUND OF THE INVENTION

The present invention relates to a brake system on a motor vehicle forbraking a pair of laterally spaced road wheels thereof which are coupledto each other through a differential.

Various brake mechanisms have heretofore been employed in combinationwith laterally spaced road wheels of motor vehicles. The brakemechanisms associated with the respective laterally spaced road wheelsshould produce well balanced braking forces which will be applied to theroad wheels. If these braking forces were out of balance, the roadwheels would be braked with braking forces of different intensity andthe motor vehicle could not be braked properly. Therefore, a relativelycomplex maintenance procedure including a number of adjusting steps hasbeen required to keep the brake mechanisms well balanced.

For high-speed and efficient transportation of goods, there are usedmany articulated trucks comprising a trailer for carrying a load and atractor for hauling the trailer, the tractor being equipped with a drivepower unit such as an engine.

The height and length of trailers are limited within certain dimensionsaccording to traffic regulations. In order for the trailers to carry amaximum amount possible of cargo, therefore, the tires of the trailersshould be of a minimum size required.

Since no drive power unit is mounted on a trailer, brake mechanisms forbraking the independently rotatable, laterally spaced road wheels on thetrailer are necessarily of limited dimensions. With the brake mechanismsthus dimensionally limited, the brake linings used in the brakemechanisms tend to wear soon, i.e., have a short service life, andtherefore must be replaced at short intervals.

SUMMARY OF THE INVENTION

According to the present invention, a differential includes a planetgear through which two shafts coupled to laterally spaced road wheels ofa motor vehicle are interconnected, and the planet gear has a rotatableshaft with a brake mechanism coupled thereto. A braking force producedby the brake mechanism is transmitted through the differential to theroad wheels depending on the rotational speeds of the road wheels. Asingle brake system including the above brake mechanism is enough forbraking the road wheels. Heretofore, however, each of the road wheelshas been associated with its own brake mechanism.

The brake system of the present invention is free of the conventionalproblem that it is difficult to keep the braking forces applied to theroad wheels well in balance. The brake system of the invention is alsoadvantageous in that it is not subject to limitations on location andsize. Therefore, a maintenance procedure for the brake system issimplified, and consumable parts of the brake system will be replaced atlonger intervals.

The brake system may comprise a turbine or a hydraulic pump forgenerating a resistive force which can be used as a braking force. Withthe turbine or hydraulic pump employed, no consumable parts are requiredby the brake system, so that the brake system maintenance can beperformed in a reduced number of steps.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a motor vehicle brake system according toan embodiment of the present invention;

FIG. 2 is a schematic view of a motor vehicle brake system of theinvention which is incorporated in a two-axle motor vehicle;

FIG. 3 is a plan view of a brake mechanism according to the presentinvention; and

FIG. 3(a) is a plan view of a known differential mechanism to which thepresent invention may be coupled;

FIG. 4 is a view of another brake mechanism according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 schematically shows a motor vehicle brake system according to anembodiment of the present invention.

An articulated motor vehicle shown in FIG. 1 includes a tractor 1 withan engine 11 mounted thereon, and a trailer 2 connected to the rear endof and hauled by the tractor 1. Road wheels rotatably supported on thetractor 1 are driven by the torque produced by the engine 11 to pull thetrailer 2.

Rotative power from the engine 11 is changed in speed by a geartransmission 13 and then transmitted through a differential 14 to theroad wheels 12.

As shown in FIG. 3(a), the differential 14 is of a known constructionand includes a speed reducer mechanism which comprises a drive pinion 44to which the torque from the engine 11 is transmitted by differentialshaft A and a ring gear 46 meshing with the drive pinion 44 and adifferential mechanism comprising differential pinions 47 coupled byrotatable shafts to the ring gear 46 and serving as planet gears, andside gears 48 coupled as sun gears to axle shafts 50 and 52 of the roadwheels 12. The differential 14 splits the torque transmitted from theengine 1 to the drive pinion and transmits the split torques to the roadwheels 12 through the side gears 48, depending on the difference betweenrotational speeds of the road wheels 12 when the motor vehicle makes aturn or runs on rough terrain. Each of the road wheels 12 is associatedwith a brake mechanism.

The trailer 2 has a coupling 21 on its front end which engages a pin 15on the rear end of the tractor 1. The trailer 2 is hauled by the tractor1 through the coupling 21.

The trailer 2 has a pair of laterally spaced road wheels 22interconnected by a differential 23 which is identical in structure tothe differential 14 on the tractor 1. The road wheels 22 are connectedto the respective side gears of the differential 23. A brake mechanism24 is mounted on the rotatable shaft of the drive pinion of thedifferential 23.

FIG. 2 schematically illustrates a two-axle trailer 3 which incorporatesa brake system of the present invention. The trailer 3 has twodifferentials 31, 32, a pair of laterally spaced road wheels 33interconnected by the differential 31, and a pair of laterally spacedroad wheels 34 interconnected by the differential 32. The trailer 3 ishauled by a tractor 1' similar to the tractor 1 (FIG. 1) through acoupling 35.

The differentials 31, 32 are structurally identical to the differential23 (FIG. 1) and have drive pinions whose rotational shafts are connectedto a two-axle drive shaft 36. A brake mechanism 37, which is identicalin construction to the brake mechanism 24 (FIG. 1), is mounted on oneend of the drive shaft 36.

The brake mechanism 24 will be described in detail below. The brakemechanism 37 will not be described as it is identical to the brakemechanism 24.

FIG. 3 shows the brake mechanism 24 in detail. A shaft A to be braked,corresponding to the rotational shaft (differential shaft) of the drivepinion of the differential 23, supports a gear A1 thereon.

The brake mechanism 24 has a friction clutch mechanism B for selectivelyconnecting and disconnecting the rotational shaft of a gear B1 meshingwith the gear A1 and the rotational shaft of a gear B2. The gear B2 isheld in mesh with a gear C1 which has a smaller number of gear teeththan the gear B2. The gear C1 is coaxially coupled to a gear C2 throughan idler shaft C. The gear C2 has a larger number of gear teeth than thegear C1.

A turbine D serves to compress air introduced from an inlet port D2 anddischarge the compressed air via an exhaust port (not shown). Theturbine D has a rotational shaft on which a gear D1 is mounted. The gearD1 is held in mesh with the gear C2 and has a smaller number of gearteeth than the gear C2.

The brake mechanism 24 operates as follows:

The trailer 2 coupled to the tractor 1 through the coupling 21 runs bybeing hauled by the tractor 1. To brake the motor vehicle while it isrunning, the brake mechanisms associated with the road wheels 12 areoperated, and the brake mechanism 24 on the trailer 2 is also operated.

More specifically, the clutch mechanism B is engaged, and rotative powertransmitted from the shaft A which is rotating is increased in speed bythe gear mechanism shown in FIG. 3 and applied to the turbine D to drivethe turbine D. The rotatable shaft of the turbine D is rotated to rotatethe impeller of the turbine D. The rotating impeller produces aresistive force which is then amplified by the gear mechanism of thebrake mechanism, and the amplified resistive force is applied as abraking force to the shaft A. The braking force acting on the shaft A,i.e., the rotatable shaft of the drive pinion of the differential 23, istransmitted through the differential 23 to the road wheels 22 dependingon the rotational speeds of the road wheels 22.

Therefore, even when the motor vehicle is braked while it is making aturn or running on rough terrain, smooth braking forces are applied tothe respective road wheels 22 according to the difference between therotational speeds of the road wheels 22.

To brake the two-axle trailer 3 shown in FIG. 2, the two-axle driveshaft 36 is braked by the brake mechanism 37, thereby transmittingbraking forces to the road wheels 33 through the differential 31 and tothe road wheels 34 through the differential 32. The tractor 1 or 1' isdecelerated by the braking forces applied to the road wheels 12 by theirassociated brake mechanisms.

FIG. 4 shows another brake mechanism according to the present invention.

A shaft A to be braked corresponds to the rotatable shaft of the drivepinion of the differential 23 shown in FIG. 1. A hydraulic pump 41 isdirectly connected to the shaft A and actuatable thereby. The hydraulicpump 41 has an inlet port connected to an oil tank and an outlet portconnected to the oil tank through a variable restriction or resistance42. The hydraulic pump 41 and the variable restriction 42 jointly serveas a hydraulic damper for dampening the rotation of the shaft A.

Operation of the brake mechanism shown in FIG. 4 is as follows:

When the motor vehicle is not braked, i.e., the brake mechanism is notactuated, the variable restriction 42 is opened to its maximum openingto minimize the resistance to the flow of working oil from the pump 41to the tank. Since the working oil discharged from the pump 41 flows tothe tank unobstructedly, no substantial energy is consumed by the pump41. Therefore, no braking force is applied to the shaft A by the pump41.

To brake the shaft A, a control signal is applied to the variablerestriction 42 to gradually close the passage therethrough of theworking oil. Therefore, the resistance to the flow of working oildischarged from the pump 41 is increased. Since the pump 41 has todischarge working oil in opposition to the resistance presented by thevariable restriction 42, substantial energy is consumed by the pump 41.Inasmuch as the consumed energy comes from the rotative power of theshaft A, the pump 41 serves to apply a braking force to the shaft A.

The braking force can be controlled by increasing or decreasing theresistance of the variable restriction 42 to the flow of working oildischarged from the pump 41. Consequently, when a large braking force isrequired, the resistance to the flow of working oil may be increased,and when a small braking force is required, the resistance to the flowof working oil may be reduced.

The hydraulic pump 41 may comprise a rotary-type pump, areciprocating-type pump, or any of various other hydraulic pumps.

Although certain preferred embodiments have been shown and described, itshould be understood that many changes and modifications may be madetherein without departing from the scope of the appended claims.

What is claimed is:
 1. A brake system in a motor vehicle having a pairof laterally spaced road wheels, comprising:a differentialinterconnecting the road wheels, said differential including two sungears coupled respectively to the road wheels, and a planet gear meshingwith said sun gears, said planet gear having a rotatable shaft; adifferential shaft meshing with said rotatable shaft of said planetgear; and braking means including a hydraulic pump having a vacuum sideand a pressure side and being directly coupled to said differentialshaft and a variable resistance connected to the pressure side of saidhydraulic pump, for variably controlling the rate of flow of working oildischarged from said hydraulic pump so that a braking force is exertedon the differential shaft in proportion to the rate of discharge flow ofworking oil from the pressure side of the hydraulic pump.
 2. A brakesystem according to claim 1, wherein said motor vehicle has two pairs oflaterally spaced road wheels, including a pair of differentialsinterconnecting the road wheels in the respective pairs.
 3. A brakesystem in a motor vehicle having at least a pair of laterally spacedroad wheels, comprising:a differential having a power input shaft, firstand second power output axial shafts, and a drive train operativelycoupling the power input shaft to the first and second power outputshafts; and hydraulic means, driven by and coupled to the power inputshaft, for applying a braking force directly to the power input shaft inproportion to a flow rate of fluid through the hydraulic means.
 4. Abrake system according to claim 3, wherein the hydraulic means comprisesa hydraulic pump having a vacuum side and a pressure side and beingdirectly coupled to the power input shaft and a variable resistancemember connected to the pressure side of the hydraulic pump for variablycontrolling the rate of flow of working oil discharged from thehydraulic pump so that a braking force is exerted on the power inputshaft in proportion to the rate of discharge flow of working oil fromthe pressure side of the hydraulic pump.